Dimensions of spheres are wrong
This is because it is not a perfect sphere, it is constructed of flat faces and it is not perfectly symmetrical. ( could have a vertex at the top and a flat face at the bottom), to get it  close to the dimensions you want increase the resolution of the sphere (segments and rings ).

just consider a simple case of a circle since it is made of finite straight lines its dimension wouldn't be as expected depending on its resolution :



you can clearly see why X differ from Y for this circle.